Geographic dimorphism of the wild silkworm, Bombyx mandarina, in the chromosome number and the occurrence of a retroposon-like insertion in the arylphorin gene

Individuals of the wild silkworm, Bombyx mandarina, collected in South Kore a (Taegu City) and Japan (Tsushima Islands and Fukuoka City) had the chromo some number of 2n = 54, while those collected in China (Hangzhou City) had the chromosome number of 2n = 56. Analysis by PCR (polymerase chain reactio n) showed that the 66-bp-long retroposon-like insertion known in the arylph orin gene was present in the B. mandarina specimens with 2n = 54, but not i n those with 2n = 56. Thus, dimorphism in the chromosome number coincided w ith the occurrence of the insertion. It is likely that the boundary dividin g the two geographic B. mandarina populations lies somewhere in the norther n part of the Korean Peninsula.